This invention relates to the production of continuous glass fibers, e.g., fibers made by melting particulate batch ingredients or minerals, including basalt and the like, and, more particularly, to the monitoring of the average diameter of such fibers.
It is well known in the art that continuous glass fibers can be produced by attenuating a plurality of streams of molten glass into fibers, collecting the fibers into a strand and winding the strand into a package for subsequent use in manufacturing various products. The molten glass flows from a furnace and through a forehearth into a feeder or bushing which has a plurality of orifices formed therein. The molten glass flows from the orifices as streams which are pulled downwardly at a high rate of speed for attenuation into fibers. A plurality of the attenuated fibers are then gathered together into a strand, coated with a sizing and wound onto a collection tube on a winder collet.
The prior art has employed various systems to control the rotational speed of the winder collet in an attempt to maintain a uniform rate of attenuation and hence produce fibers which are closely similar in diameter and which have a uniform diameter throughout their length. The diameter of a package gradually increases as the strand is wound onto the collection tube; therefore, the rotational speed of the collet must be simultaneously decreased in order to maintain a constant rate of attenuation. Roberson, U.S. Pat. No. 3,265,476, discloses varying the winding speed at a programmed or patterned rate so that the pull speed or strand speed is approximately constant. An alternative method of controlling fiber diameter is disclosed in Roberson, U.S. Pat. No. 3,126,268, in which the set point temperature of the bushing is varied at a programmed or patterned rate to compensate for the increasing winding speed as the package is being built.
While such control systems give satisfactory results and represent a marked improvement over the control systems previously known in the art, the fiber monitoring system of Shofner et al., as described in the U.S. patent application of Shofner, Greene and Hanna, Ser. No. 178,269, filed Aug. 15, 1980 can produce even more uniform fibers. Such fiber monitoring system utilizes: a source of electromagnetic radiation, such as a light-emitting diode; beam forming optics to form the electromagnetic radiation into a beam for impingement upon the fibers of interest; collection optics for collecting the radiation scattered by the fibers and for focusing such radiation on a detector to generate a signal indicative of the average fiber diameter. This signal may then be used to modify one or more of the process variables, such as winding speed, to produce fibers of a predetermined average fiber diameter. However, it has been found that a signal of the same magnitude may be generated for several different average fiber diameters, thus resulting in a non-monotonic response.
Therefore, it is an object of this invention to provide a method of and apparatus for monitoring a fiber or fibers that produces a monotonic response for collected, backscattered radiation versus average fiber diameter.